Only hydrogenated NBR having an iodine number of 28 or less has been so far used for fear of heat resistance problem, etc., where the heat resistance can be indeed improved, but it cannot be disregard that there is still a possibility to deteriorate the low temperature characteristics (as evaluated in terms of compression set value at low temperatures such as −30° C.). As a result, the molded products will suffer from occurrence of permanent set, when exposed to low-temperature using circumstances and oil leakage therefrom will take place, especially in the case of a sealing materials, leading to undesirable failure in product performance.
Patent Literature 1: JP-A-2001-288303
The present applicant has so far proposed a hydrogenated NBR composition capable of giving molding products, which satisfy both heat resistance and cold resistance at the same time, which comprises a hydrogenated NBR having an acrylonitrile content of 15-30% by weight, white carbon having a specific surface area of 200 m2/g or less, and an organic peroxide, and preferably further contains a polyfunctional unsaturated compound and/or carbon black. The proposed hydrogenated NBR composition could attain the expected results, but encountered such a new problem as swelling of the polymer due to the low acrylonitrile content in such use circumstances that the gaskets around engines were exposed to oils and fuel oils, resulting in use failure.
Patent Literature 2: JP-A-2000-212333
The present applicant has further proposed a hydrogenated NBR composition, which comprises 100 parts by weight of a hydrogenated NBR having an acrylonitrile content of 25-44 and an iodine number of 32-65, 2-23 parts by weight of an ester-based plasticizer, and 0.5-10 parts by weight of an organic peroxide, and preferably further contains 0.5-10 parts by weight of a polyfunctional unsaturated compound, as a hydrogenated NBR composition capable of giving molding products having distinguished oil resistance and fuel oil resistance as well as distinguished heat resistance and cold resistance, and also capable of serving as suitable molding materials for intake manifold gaskets of automobile engines.
Patent Literature 3: WO 2007/094158 A1
The proposed hydrogenated NBR can fully attain the desired object, but fails to satisfy a cost performance, because of use of expensive hydrogenated NBR as a rubber component.